Sonochemical synthesis of supersaturated Ga–Al liquid-alloy fine particles and Al3+-doped γ-Ga2O3 nanoparticles by direct oxidation at near room temperature

[Display omitted] •Supersaturated gallium (Ga)–aluminum (Al) liquid alloy microparticles (Dav = 1.72 µm) was synthesized at 60 °C by ultrasound irradiation.•Al3+-doped γ-Ga2O3 nanoparticles (NPs) with small particles size (Dav = 59 nm) and high specific surface area (SBET = 181 m2/g) were obtained at 60 °C without dispersant and leftover counter anions using ultrasound effects.•The oxidation of liquid Ga was remarkably accelerated at 60 °C by alloying with metallic Al and ultrasound irradiation.•The lattice constant unchanged by Al3+-doping, indicating Al3+ cations were incorporated into defects site of γ-Ga2O3 due to nonequilibrium reaction fields provided by ultrasound.•Al3+-doped γ-Ga2O3 NPs were synthesized by sonochemical methods orienting sustainable development goals (SDGs). In this study, we investigated the fabrication of supersaturated gallium (Ga)–aluminum (Al) liquid alloy and Al3+-doped γ-Ga2O3 nanoparticles (NPs) at near room temperature (60 °C) using sonochemical and sonophysical effects. Supersaturated Ga–Al liquid alloy microparticles (Dav = 1.72 µm) were formed and stabilized at 60 °C by the thermal nonequilibrium field provided by sonochemical hot spots. Compared with liquid Ga, supersaturated Ga–Al liquid alloy was rapidly oxidized to a uniform oxide without Al2O3 or Al deposition. Thus, ultrafine Al3+-doped γ-Ga2O3 NPs were obtained after only 1 h of ultrasonic irradiation at 60 °C. The oxidation of liquid Ga was remarkably accelerated by alloying with metallic Al and ultrasonic irradiation, and the time was shortened. The average diameter and surface area of the γ-Ga2O3-based NPs were 59 nm and 181 m2/g, respectively. Compared with γ-Ga2O3, the optical bandgap of the Al3+-doped γ-Ga2O3 NPs was broadened, and the thermal stability improved, indicating Al3+-doping into the γ-Ga2O3 lattice. However, the lattice constant of γ-Ga2O3 was almost unchanged with or without Al3+-doping. Al3+ was introduced into the defect sites of Ga3+, which were massively induced in the defective spinel structure during ultrasonic processing. Therefore, sonochemical processing, which provides nonequilibrium reaction fields, is suitable for the synthesis of supersaturated and metastable materials in metals and ceramics fields.